In any electronic assembly, it is necessary to provide adequate cooling for heat-generating electronic components to maintain their temperatures within acceptable limits. Failure to maintain proper component temperature can result in incorrect operation as well as reduced component lifetime. In the case of a packaged integrated circuit, the temperature limit is often specified as a maximum "case" temperature, i.e., the maximum allowed temperature of the exterior surface of the package. Maintaining the case below this temperature ensures that the semiconductor devices on the integrated circuit within the package operate below a corresponding acceptable maximum temperature.
A very common and effective way of cooling electronics assemblies is forced-air convection cooling, in which a fan is used to blow cool air over heat-generating components. In many types of electronics assemblies, however, such a cooling scheme is not feasible. For example, portable electronics assemblies, such as portable computers, are generally designed for compactness. These assemblies cannot afford the luxury of space for air flow, a bulky fan, and the need for a bigger power supply to power the fan.
An alternative cooling scheme that is generally used in compact electronics assemblies is conduction cooling. In this scheme, heat from heat-generating devices is conducted away via thermally-conductive structures that contact the devices. An example might be a metal heatsink member that channels heat from an integrated circuit to the frame of an enclosure. The heat is then channeled to larger, exposed areas of the assembly, which in turn can be cooled by passive convection, i.e., exposure to ambient air, or by radiation of the heat into free space.
While conduction cooling is effective and widely used in compact assemblies, it is generally not as efficient as convection cooling. As a result, devices used in compact assemblies generally are not allowed to generate as much heat as they might when used in larger, convection-cooled assemblies. This limitation on heat generation directly translates to a limitation on the power consumption of the devices. This power limitation in turn becomes a limitation on the functional density and speed of the devices, because as a generally rule a denser, faster device consumes more power. This is particularly true regarding digital logic devices such as central-processing unit (CPU) chips. Accordingly, compact electronics assemblies typically have lower performance than larger, convection-cooled assemblies having otherwise similar components. A good example of this dichotomy is the performance distinction between desktop and portable personal computers.
In order to increase the performance of compact electronics assemblies, then, the mechanical designer is challenged to increase conductive cooling efficiency so that higher-power devices may be used. It is to this general problem of improving the conductive cooling of heat-generating devices that the present invention is directed.